Field of the Invention
The present invention relates to a water heater and particularly to a water heater of a latent heat recovery type capable of heating water by recovering latent heat of combustion gas.
Description of the Background Art
In addition to a primary heat exchanger for mainly recovering sensible heat of combustion gas, a water heater of a latent heat recovery type includes a secondary heat exchanger for mainly recovering latent heat. This water heater of a latent heat recovery type can obtain condensation heat (latent heat) by condensing water vapor contained in combustion gas, so that it can achieve relatively high thermal conversion efficiency.
According to such a water heater of a latent heat recovery type, condensation of water vapor occurs in combustion gas within the secondary heat exchanger, thereby producing drainage water (dew condensation water). At this time, combustion gas contains nitrogen oxides generated by reaction between nitrogen and oxygen in the air due to combustion, sulfur oxides generated by reaction between oxygen and the sulfur content in the fuel due to combustion, and the like. Accordingly, the produced drainage water is strongly acid due to these nitrogen oxides and sulfur oxides.
The drainage water produced in the secondary heat exchanger is generally neutralized in a neutralizer disposed in a drainage water discharge path, and then, discharged through the drainage water discharge path to the outside. The water heater provided with such a drainage water discharge path has a configuration in which a combustion gas flow path and a drainage water discharge path communicate with each other.
Accordingly, in the case where a water heater of a forced exhaust type serving to force the outside air inside by a fan to thereby emit combustion gas to the outside is disposed inside the building, positive pressure occurs in the secondary heat exchanger. This may cause a problem that combustion gas that should originally be emitted to the outside of the building through an exhaust pipe (a B vent) is emitted through the drainage water discharge path to the inside of the building in which a water heater is arranged.
Furthermore, for example, in the case of a water heater of a latent heat recovery type using an exhaust suction system as disclosed in Japanese Patent Laying-Open No. 60-186617 and Japanese Patent Publication No. 06-35897, since a fan is arranged downstream of the secondary heat exchanger, negative pressure occurs in the secondary heat exchanger due to suction pressure of the fan, which causes the outside air to flow through the drainage water discharge path back into the secondary heat exchanger. Consequently, it may become difficult to cause the drainage water to be discharged from the secondary heat exchanger.
Thus, in such a water heater, for example, a plurality of chambers are provided within a drainage water tank disposed in the drainage water discharge path, and holes allowing communication between these chambers are filled with drainage water and thereby water-sealed, so as to solve the above-described problem. Such a water-sealing structure of the drainage water discharge path in the water heater of a latent heat recovery type is disclosed, for example, in Japanese Patent Laying-Open No. 2008-298367 and Japanese Patent Laying-Open No. 2013-160453.
However, even in the case of the water heater provided with a drainage water discharge path having a water-sealing mechanism, when performing a trial operation of a new water heater, or when resuming an operation of a water heater that has not been used for a long period of time or resuming an operation of a water heater or the like from which drainage water is removed for maintenance or freeze proofing, there occur problems that combustion gas in the water heater of a latent heat recovery type using a forced exhaust system described above flows into the building and the drainage water is difficult to be discharged from the secondary heat exchanger in the water heater of a latent heat recovery type using an exhaust suction system, for a time period from start of the operation until the drainage water discharge path is water-sealed.